Antennas are one of the components in a wireless system infrastructure that are used to transfer information between two different points in space. The antenna is a transducer that transforms currents and voltages in circuits into electric and magnetic fields in free space and vice-versa. These electric and magnetic fields propagate in free space; in addition, these fields can be modulated to carry information. Wireless signals carry information that is launched/captured into/from free space by an antenna.
Some examples of UWB (Ultra-Wideband) antennas that are used in the field include a dipole whip or rod, a printed PCB (Printed Circuit Board) wide dipole/monopole, or a ceramic omni-directional UWB antenna. Several different examples are provided. FIGS. 1a through 1c illustrate different examples of printed PCB dipole UWB antennas using different shapes for the dipole portion of the antenna. Typically, a solid metallic plane or surface is perpendicular to the axis of the main radiation beam. In FIG. 1a, a dipole 1-1a uses ovals 1-2a and 1-3a for the dipole elements. The dipole is a center fed driven structure as indicated by 1-4a where the structure is balanced and consists of the two conducting co-planar ovals 1-2a and 1-3a. The transceiver (not shown) would be connected to the center 1-4a of the antenna (in addition, a switch, an integrated transceiver IC, and/or a tuning network may be inserted between these components).
An example using rectangular elements for the UWB dipole 1-1b is illustrated in FIG. 1b. The center feed 1-4b is connected to the rectangular dipoles 1-2b and 1-3b. Triangular elements 1-2c and 1-3c are the dipole elements which are fed by the feed point 1-4c as indicated in FIG. 1c. Several different polygon shapes were illustrated in FIG. 1a through 1c indicating that the dipole elements can have various polygon shapes. However, the final dipole element needs to be optimized in shape and size for proper UWB operation.
Another antenna type can include a planar reflector (usually formed from an antenna ground) can be designed to form quasi-Yagi antenna structures in PCBs. An example is illustrated in FIG. 2a which depicts a double sided PWB. The metallization on the top side is the solid color while the cross-hatched pattern is the metallization on the bottom side of the PWB.
Although not indicated, the PWB could be a multi-layer board. The additional layers can be patterned into reflector plates to form multiple reflectors for the Multiple Planar Reflector Ultra-Wide Band (UWB) Antenna.
FIG. 2a shows a patterned layout that is used to form a quasi-Yagi antenna 2-1. A PWB 2-2 has a dipole 2-3 and a director 2-4 that is formed on the same top side of the board. The cross-hatch area is the ground plane reflector 2-5 formed on the bottom side of the board. The feed point 2-6 identifies where the transceiver would be connected.
FIG. 2b shows a patterned layout that is used to form a different quasi-Yagi antenna 2-7. A PWB 2-2 has a dipole 2-3 but in this case the director is eliminated. A ground plane formed on the bottom side below the Yagi feedpoint 2-6 that is cross-hatched becomes part of the reflector 2-5. The feed point 2-6 identifies where the transceiver would be connected.
FIG. 2c illustrates a dipole antenna 2-8 on a PWB 2-11. The two metallic rectangular sections 2-9 and 2-10 form the dipole elements.
In FIG. 2d, the structure 2-12 as indicated in Lin et al., U.S. Pat. No. 7,064,728, is an ultra-wideband dipole antenna 2 in accordance with a first preferred embodiment of the invention comprising a generally axially disposed first outer metal sleeve 20 having a closed face 201 at a top end thereof opposite its open bottom end, and a hole 202 through the closed face 201; a generally axially disposed intermediate metal sleeve 22 dimensioned to be surrounded by the first outer metal sleeve 20, the intermediate metal sleeve 22 having a closed face 221 at a top end thereof opposite its open bottom end, and a hole 222 through the closed face 221; a generally axially disposed second outer metal sleeve 23 above the first outer metal sleeve 20, the second outer metal sleeve 23 having a closed face 231 at a bottom end thereof opposite its open top end; a conductive interconnection 24 having a bottom end 241 extended through the hole 202, a feed point location 243 at the bottom end 241, and a top end 242 electrically connected to the closed face 231; and an inner coaxial conductor 25 surrounded by the intermediate metal sleeve 22, the coaxial conductor 25 including a central conductor 251 electrically connected to the feed point location 243 and an outer grounding sleeve 252 surrounding the central conductor 251 and electrically connected to edges of the hole 222.
In addition, there is the three-dimensional parabolic reflector antenna. The parabolic surface focuses the reflected incoming energy into a focal point or emits outgoing energy from the focal point to the parabolic surface forming a narrow beam emitted from the antenna. The transceiver is positioned at the focal point to receive or transmit a desired signal. The parabolic antenna is bulky, heavy and costly.
A desirable feature would be to increase the directivity of an antenna without necessarily increasing the cost or weight of the system. A need of building a high-gain directional antenna for the receive and transmit paths of a transceiver is highly desirable. This greatly increases the received/transmitted powers and thus increases the operating range of a low-power wireless system. Another benefit is that the wireless data transmission rate can be improved providing higher signal bandwidths.